Use of a multi-start screw thread in an ex-d housing

Abstract

The present disclosure relates to a field device of automation technology, including a housing with an opening for accommodating field device components, wherein the housing has at an edge of the opening a first screw thread, a lid for closing the opening of the housing, wherein the lid has at an edge of the lid a second screw thread, wherein the first and second screw threads are embodied to be complementary to one another, so that the housing after closing with the lid in assembly fulfills all Ex-d requirements, wherein the first and second screw threads are embodied as multi-start threads.

1 . A field device of automation technology, comprising:
 a housing configured to accommodate field device components, wherein the housing includes an opening in a side of the housing and, at an edge of the opening, a first screw thread in an axial direction; and   a lid configured to close the opening of the housing in assembly with the housing, wherein the lid includes a side wall defining a second screw thread in the axial direction from an edge of the lid,   wherein the first screw thread and the second screw thread are complementary to each other and define a gap length in the axial direction having a flame propagation resistance over the gap length such that the assembly of the housing and lid meet the requirements for explosion protection by explosion-proof and/or flameproof encapsulation as defined by an Ex-d industry standard, and   wherein the first screw thread and the second screw thread are each configured as multi-start threads having two or more intertwined threads running in parallel to one another.   
     
     
         2 . The field device of  claim 1 , wherein the first screw thread and the second screw thread are each embodied as four-start threads. 
     
     
         3 . The field device of  claim 1 , wherein the first screw thread and the second screw thread have axially at least five thread crests. 
     
     
         4 . The field device of  claim 1 , wherein the first screw thread and the second screw thread have axially at least eight thread crests. 
     
     
         5 . A lid-closing mechanism of a field device of automation technology, comprising:
 a housing configured to house field device components, the housing including an opening in a housing wall, the opening having an edge from which a first screw thread extends along the wall in an axial direction; and   a lid adapted to close the opening of the housing in assembly with the housing, the lid including a side wall having an edge from which a second screw thread extends along the side wall in the axial direction,   wherein the first screw thread and the second screw thread are complementary and define a gap length of the opening such that, when the opening is closed by the lid, the field device fulfills requirements of flame propagation resistance over the gap length according to requirements for explosion protection by explosion-proof and/or flameproof encapsulation as defined in Ex-d industry standard IEC 60079-1, and   wherein the first screw thread and the second screw thread are each multi-start screw threads having two or more intertwined threads running in parallel to one another.   
     
     
         6 . The lid-closing mechanism of  claim 5 , wherein the first screw thread and the second screw thread are embodied as four-start threads. 
     
     
         7 . The lid-closing mechanism of  claim 5 , wherein the first screw thread and the second screw thread have axially at least five thread crests. 
     
     
         8 . The lid-closing mechanism of  claim 5 , wherein the first screw thread and the second screw thread have axially at least eight thread crests.